Auxiliary orthodontic appliance

ABSTRACT

Auxiliary orthodontic appliance, namely expansion screw for the maxilla or mandible, bracket or buccal tube, which in order to improve its properties consists of titanium or an alloy on the basis of titanium and the surfaces of which are formed by a titanium oxide skin.

BACKGROUND OF THE INVENTION

The invention relates to an auxiliary orthodontic appliance for humanbeings. This may be an auxiliary orthodontic or orthopaedic appliancefor the maxilla or mandible. As used in technical terminology, such anauxiliary appliance is an article in the form of an expansion screw, abracket, a buccal tube or a ring-shaped tooth band which remains in themouth for a limited amount of time. Expansion screws are used forexpanding the human jaw and also for correcting the position of one orseveral teeth. Brackets and buccal tubes also serve to correct theposition of the teeth and are attached to the teeth, in the givencircumstances, by means of a ring-shaped band which surrounds thepertinent tooth.

An expansion screw usually consists of two screw body parts and athreaded spindle which has threads running in opposite directions oneither side of a spindle head at the center of the threaded spindle andengages corresponding threaded bores of the two screw body parts so thatthe two screw body parts are adjustable relative to one another byturning the threaded spindle. In the given circumstances, guide means,in particular, in the form of guide pins, can also be provided toprevent the two screw body parts from twisting in opposite directionswhen the threaded spindle is turned. The various parts of expansionscrews known so far consist of stainless steel or nickel-silver alloys.Stainless steel was also used for the manufacture of brackets and buccaltubes, but ceramic and plastic brackets are also known, however, theseare not fully satisfactory with respect to their strength.

Although it has been known for a long time that stainless steel andnickel-silver are not sufficiently resistant to corrosion for thesepurposes and, in particular, can cause allergic reactions on account oftheir nickel content, so far not a single manufacturer of such auxiliaryappliances anywhere in the world has marketed expansion screws, bracketsor buccal tubes which do not have the disadvantages explained above.

As the auxiliary appliances in question are worn in the mouth, theprevention of electrochemical corrosion of the auxiliary applianceconstitutes quite a considerable problem. For example, in view ofamalgam tooth fillings, the metallic auxiliary appliances known so farhave also not proven fully satisfactory in this respect. In the case ofexpansion screws made of nickel-silver with guide pins and threadedspindles made of stainless steel, for example, the electrochemicalcorrosion can occur within a few days if the parts made of nickel-silverare not protected by a chrome or nickel coating.

SUMMARY OF THE INVENTION

The object underlying the invention was to create auxiliary appliancesof the kind in question which do not lead to problems even if the wearerhas already undergone restorative dental treatment, and in accordancewith the invention this object is accomplished by the auxiliaryappliance consisting of titanium or an alloy on the basis of titaniumand its surfaces being formed by a titanium oxide skin whose electricalbreakdown potential in synthetic saliva with a pH value of 2.3 at 37° C.is greater than 2000 mV.

Titanium and titanium alloys have been in use for a long time forhigh-quality technical parts such as, for example, watch cases, andowing to their biocompatibility also as materials for implants. However,in spite of the difficulties indicated hereinabove and known for a longtime, so far expansion screws, brackets and buccal tubes have never beenmade of titanium or alloys on the basis of titanium anywhere in theworld. These auxiliary orthodontic appliances are distinct mass-producedarticles in the manufacture of which these materials have not gainedaccess although titanium and its alloys can be worked in an absolutelyeconomical way by the available cutting tools, titanium and its alloysare obtainable as fine powders so the auxiliarly appliances an questioncan also be manufactured economically by metal injection molds, andalthough molding materials are available to allow titanium and itsalloys to also be castable economically in a precision casting process.

Surprisingly it was ascertained that a titanium oxide skin as definedhereinabove passivates the inventive auxiliary appliances to be worn inthe mouth sufficiently even if the wearer also has teeth which areprovided with an artificial part consisting of an alloy with a high goldcontent, which can be added as a further advantage to the knownbiocompatibility of titanium and alloys on the basis of titanium.

To measure the breakdown potential of the oxide skin which isproducible, for example, by anodic oxidation or annealing in anatmosphere containing oxygen, synthetic saliva according to GermanIndustrial Standard 13912 and a measuring cell according to ASTM (seeG5-Rec. Practice for Standard Reference Method for making Potentiostaticand Potentiodynamic Anodic Polarisation Measurements, 1980 Annual Bookof ASTM Standard, Part 10) should be used; in this connection referenceis also made to the essay "Grundsatzliches zur Methodikpotentiodynamischer Polarisationsmessungen an Dentallegierungen inkustlichen Speicheln" (Basics on the method of potentiodynamicpolarisation measurements of dental alloys in artificial salivas) by J.Geis-Gerstorfer and H. Weber, Deutsche Zahnarztliche Zeitschrift (Germandentists' magazine) 42, 1987, pages 91-97.

Alloys on the basis of titanium are to be understood as high-alloytitanium alloys according to German Industrial Standard 17851.

A particular advantage of the inventive measure is obtained withexpansion screws in which higher demands have to be made on the strengthof the threaded spindle than on that of the screw body parts. In knownexpansion screws with a threaded spindle made of a material of higherstrength than the screw body parts, the galvanic corrosion of the partsmade of nickel-silver could only be reduced by coating them with nickelor chrome. With an inventive expansion screw, on the other hand, therespectively required strength of screw body parts and threaded spindleis achieved solely by the choice of different, standardized degrees ofpurity of the titanium without this causing differences in theelectrochemical series (titanium is available on the market in fourdifferent standardized degrees of purity according to German IndustrialStandard 17850--grades 1 to 4--which differ in their strength, moreparticularly, titanium of a lower degree of purity has a greaterstrength than purer titanium and so, for example, grade 4 titanium isused for the threaded spindle of an expansion screw according to theinvention, whereas, for example, grade 1 or 2 titanium can be used forthe screw body parts. Nevertheless, there is never any allergy risk withan expansion screw according to the invention, which is not the casewith the known expansion screws made of stainless steel or ofnickel-silver with a nickel coating.

BRIEF DESCRIPTION OF THE DRAWINGS

Three embodiments of the auxiliary appliance according to the inventionare shown in perspective illustrations in the appended drawings, moreparticularly, in

FIG. 1: an expansion screw, in

FIG. 2: a bracket and in

FIG. 3: a buccal tube.

DESCRIPTION OF THE INVENTION

The expansion screw shown in FIG. 1 consists of a first and a secondscrew body part 10 and 12, respectively, a threaded spindle 14 with aspindle head 16 and two guide pins 18. The threaded spindle 14 has oneither side of the spindle head 16 spindle sections 14a and 14b withthreads running in opposite directions. These engage correspondingthreaded bores of the screw body parts 10 and 12 so that the spacing ofthe two screw body parts 10, 12 from one another is adjustable byturning the threaded spindle 14. The two guide pins 18 can each be fixedin one of the two screw body parts 10, 12 as they are primarily toprevent the two screw body parts 10, 12 from twisting in oppositedirections when the threaded spindle 14 is turned. A transverse bore 16ain the spindle head 16 enables insertion of a tool for actuation of thethreaded spindle 14.

As mentioned previously, the threaded spindle 14 can consist, forexample, of grade 4 titanium, whereas the remaining parts of theexpansion screw for maxilla or mandible can consist of grade 1, 2 or 3titanium, and all of the surfaces of the various parts are coated with athin titanium oxide skin.

FIG. 2 shows a bracket designated in its entirety 20 with a base 22,FIG. 3 a buccal tube designated in its entirety 24 with a base 26 whichlike the base 22 of the bracket 20 for attaching the bracket to a tooth,serves to attach the buccal tube to a tooth. Neither the bracket nor thebuccal tube requires further description as the design of theseauxiliary appliances is known and the latter differ from the knownauxiliary appliances only in the material and in the feature that theirsurfaces are coated with a thin titanium oxide skin.

When an alloy on the basis of titanium is referred to hereinabove, thismeans that this alloy contains more than 50 per cent by weight titanium.The oxide skin can be readily obtained in an oxidizing atmosphere, andthe thickness of the oxide coating can be controlled by, for example,changing the composition of the oxidizing atmosphere, the treatmenttemperature and/or the duration of the treatment--a relatively thickoxide coating can be produced even by a short heating of the auxiliarlyappliances in air without having to accept a loss in the strength of theparts.

I claim:
 1. Auxiliary orthodontic appliance, characterized in that saidauxiliary appliance comprises at least one of titanium and an alloy onthe basis of titanium and its surfaces are formed by a titanium oxideskin whose electrical breakdown potential in synthetic saliva with a pHvalue of 2.3 at 37° C. is greater than 2000 mV.
 2. Auxiliary applianceas defined in claim 1 comprising two screw body parts adjustablerelative to one another by means of a threaded spindle, characterized inthat said threaded spindle consists of a titanium material of higherstrength than said screw body parts.
 3. Auxiliary appliance as definedin claim 2, characterized in that said threaded spindle consists oftitanium of a lower purity than said screw body parts.
 4. Auxiliaryappliance as defined in claim 1, characterized in that its componentsare in the form of injection molded parts.
 5. Auxiliary appliance asdefined in claims 1, characterized in that its components are in theform of precision castings.
 6. Auxiliary orthodontic appliance,characterized in that said auxiliary appliance comprises at least one oftitanium and an alloy on the basis of titanium and its surfaces areformed by a passivating skin comprising a compound of titanium formedin-situ on the surfaces and having an electrical breakdown potential insynthetic saliva with a pH value of 2.3 at 37° C. greater than 2000 mV.7. Auxiliary appliance as defined in claim 6 comprising two screw bodyparts adjustable relative to one another by means of a threaded spindle,characterized in that said threaded spindle consists of a titaniummaterial of higher strength than said screw body parts.
 8. Auxiliaryappliance as defined in claim 6, characterized in that said threadedspindle consists of titanium of a lower purity than said screw bodyparts.
 9. Auxiliary appliance as defined in claim 6, characterized inthat its components are in the form of injection molded parts. 10.Auxiliary appliance as defined in claim 6, characterized in that itscomponents are in the form of precision castings.